For many years, magnetrons have been commonly used in microwave ovens to generate microwave energy for the purpose of heating food, beverages, or other items. A magnetron essentially consists of a circular chamber with multiple cylindrical cavities spaced around its rim, a cathode built into the center of the chamber, and a magnet configured to generate a magnetic field. When incorporated into a microwave system, the cathode is coupled to a direct current (DC) power supply that is configured to provide a high voltage potential to the cathode. The magnetic field and the cylindrical cavities cause electrons within the cavity to induce a resonant, high-frequency radio frequency (RF) field in the cavity, and a portion of the field may be extracted from the cavity via a probe. A waveguide coupled to the probe directs the RF energy to a load. For example, in a microwave oven, the load may be a heating cavity, and the impedance of the heating cavity may be affected by objects within it.
Although magnetrons have functioned well in microwave and other applications, they are not without their disadvantages. For example, magnetrons typically require very high voltages to operate. In addition, magnetrons may be susceptible to output power degradation over extended periods of operation. Thus, the performance of systems in which magnetrons are included may degrade over time. Further, magnetrons tend to be bulky, heavy components that are sensitive to vibration, thus making their use in portable applications undesirable.
In more recent times, microwave heating apparatus have been proposed that utilize solid-state hardware to produce RF signals that are radiated into a heating cavity. The power required by solid-state microwave heating apparatus may be significantly less than the power required by magnetron-based systems. In addition, the performance of solid-state microwave heating apparatus does not degrade over time. Further, implementation of solid-state hardware enables RF signal characteristics to be varied throughout a cooking operation. Accordingly, developers seek RF signal control methods and apparatus that may improve the quality of cooking operations.